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Webcast-Catalyst9k
New Member

Load Balancing

Can someone tell me how unequal-cost load balancing works?(only with IGRP and EIGRP - i know...)

I know that equal-cost load balancing is supported on every routing protocol, and i guess it works like this: the equal-cost metrics summed up and then divided by number of routes.

unequal-cost - i have no idea though..

am i correct on this one?

5 REPLIES
Silver

Re: Load Balancing

You're right on equal-cost, for unequal-cost instead of giving all links an equal share, we give links a share proportional to their routing metric (default bandwidth and delay). More info here:

http://www.cisco.com/en/US/tech/tk365/technologies_tech_note09186a008009437d.shtml

Re: Load Balancing

With unequal cost load sharing the router would load balance traffic across multiple paths proportionate to the metric. Let's say if the router has two paths to get to destination X, one with metric 10 and another one with metric of 30. When configured to do unequal-cost load sharing the router install both paths in the routing table and load share packets on a 3:1 basis out those links based on the metric of 30/10.

I don't know if you were looking for the configuration needed to do unequal cost load sharing and if you do here's a small example to illustrate this.

router eigrp 1

variance 3

With a variance of 3 the router would install a route that has a metric inferior by up to 3 times than that of the best metric. A route that has the best metric of 10 and another path with a metric of 30 would cause the router to use both paths.

HTH

Sundar

New Member

Re: Load Balancing

so more traffic will flow on the one with metric 10 right? cos its less congested..

3:1

3 to the route with metric 10

1 to the route with metric 30

?

Re: Load Balancing

Correct.

Typically the one that's got the best metric is probably the one with more bandwidth capacity.

HTH

Sundar

New Member

Re: Load Balancing

use varience in eigrp for load balancing in unequal cost path

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